Means and method of forming piezoelectric crystals



y 11, 1944- c. w. M CONNELL 2,353,171

MEANS AND METHOD OF FORMING PIEZO-ELECTRIC CRYSTALS Filed Dec. 15, 1941 2 Sheets-Sheet l INVENTOH CHARLES w. MAc coumzu. BY

' yc mvz July 11, 1944. c, w MacCONNELL, 2,353,171

MEANS AND METHOD OF FORMING PIEZO-ELECTRIC CRYSTALS 2 Sheets-Sheet 2 INVENTOR CHARLES W. MAC CONNELL AZORNEY Filed Dep. 15, 1941 Patented July 11, 1944 MEAN-S AND METHOD OF FORMING PIEZOELECTRIC CRYSTALS Charles w. MacConnell, Southbridge, Mass., as-

signor to Harvey-Wells Communications, Inc., Southbridge, Masa, a corporation of Massachusetts Application December 15, 1941, Serial No. 423,017

7 Claims.

This invention relates to .piezo-electric crystals and more particularly to emcient and economical means and method of processing said crystals whereby their resultant frequency and output characteristics may be more simply and positively controlled.

One of the principal objects of the invention is to provide improved means and method of processing piezo-electric crystals whereby the said crystals may be madeto oscillate properly and may be more positively and economically controlled as to the frequency of said oscillations.

Another object is to provide improved means and method of lapping piezo-electric crystals whereby substantially parallel surfaces may be formed on the opposed sides of said crystals in a simple and eflicient manner.

Another object is to provide novel means and method of economically processing precision crystals of given frequency values.

Another object is to provide novel means and method of changing the frequency of a crystal which oscillates properly, but which is slightly off as to desired frequency, without materially altering its oscillating properties.

Other objects and advantages of the invention will become apparent from the following description taken in connection with the accompanying drawings and it will be apparent that many changes may be made in the details of construction, arrangement of parts and steps of the method shown and described without departing from the spirit of the invention as expressed in the accompanying claims. It is therefore desired that the invention not be limited to the exact details of construction, arrangement of parts and steps of the method shown and described as the preferred forms only have been given by way of illustration.

Referring to the drawings:

Fig. I is a perspective view of the device embodying the invention setting forth one step of the process of manufacture;

Fig. II is a sectional view taken as on line II-II of Fig. I and looking in the direction indicated by the arrows; I

Fig. III is a sectional view taken as on line IlI-lII of Fig. II looking in. the direction indicated by the arrows and showing the sectional parts in full: and

Fig. IV is a diagrammatic view illustrating a step of a modification in the method of the invention.

It has been usual in processing piezo-electric crystals to reduce the crystals to the proper size,

working characteristics and frequency by very delicate hand controlled operations which depended entirely upon the skill of the operator.

One of the difllculties in processing piezo-electric crystals of the character described has been to obtain a substantially parallel relation of the side surfaces of the crystals while simultaneously reducing said crystals to the required uniform thickness. The uniform thickness is essential in obtaining the working characteristics and frequency values desired of the crystals. Because of the necessity of exceptionally skilled labor in processing said crystals, in the past, and because of the delicate hand operations required to produce crystals of this nature, such crystals have been extremely difficult and costly to make. This was due to a great percentage of spoilage which inherently resulted from the hand controlled procedure of fabrication and is one of the many disadvantages which the present invention obviates.

Referring more particularly to the drawings wherein like characters of reference designate like parts throughout the several views the device which performs one of the essential steps of the method, as shown in Figs. I through lII, comprises broadly a lap I having a relatively flat surface 2 thereon. The said surface 2 has a plurality of communicating longitudinal grooves 3 therein which provide means into which excessive abrasive may flow from the effective surface of the lap. The piezo-electric crystal 4, which is to be lapped, is held in a holder 5 and is moved with said holder over the relatively flat surface 2 of the lap I. The relation of the crystal with the holder and lap can best be seen in Fig. II. The holder 5 comprises a main upright portion 6 having a base I with a relatively flat surface 8 thereon. The main upright portion 6 has a longitudinal opening 9 extending throughout the major portion of the length thereof with a closed end [0 adjacent the base 1. The closed end has a reduced opening ll therein communicating with the longitudinal opening 9. Internally of the opening 9 there is a pair of angularly disposed plates l2. The said plates l2 form a slideway for a slide plunger II. The said slide plunger I3 is preferably of a triangular cross section and is held in desired frictional contact with the slide plates I2 by means of a pressure plate H. The said pressure plate I4 is resiliently urged into engagement with the slide plunger l3 by pins 15 pressed toward the plate by backing springs IS. The said pins are slidably mounted within the threaded longitudinal bores ll of spaced blocks II. The blocks are attached to the upright 6 by suitable means such as pins or screws not shown. The tension of the respective backing springs I is varied by means of screws II threaded with the internally threaded bore of the blocks I4.

By adjustment of the screws Ilproper tension may be directed to the resilient backing springs I6, thereby setting up a pressure on the pins I5 suitable to retain the slide plunger I3 in different positions of adjustment longitudinally of the slide plates I2.

Theslide plunger I3, adjacent the lower end thereof, is provided with a protruding portion 20 fitting within the opening II. The protruding portion 20 has an end surface 2I which is substantially parallel with the surface 8 on the base and substantially perpendicular to the longitudinal axis of the slide plunger l3. The said slide plunger l3 has a knob-like member 22 adjacent the upper end thereof which is adapted to be engaged when it is desired to move the slide plunger I3 longitudinally of the slide plates I2. The size of the opening I I and the contour thereof depends upon the size and shape of the crystal which is to be abraded and is preferably made slightly larger than the crystal.

The procedure of forming the crystal is substantially as follows: The crystal is first cut from the mother crystal in proper desired relation to the optical axis, electrical axis and one of the crystallization axes of the mother crystal, depending upon the characteristics desired of the completed crystal. A suitable abradant such as an ordinary mixture of emery and kerosene is placed on the surface 2 of the lap. The kerosene is preferably sprayed on the surface of the lap or applied thereto by an ordinary oil cup and the emery is in powder form and is shaken onto the surface of the lap. A second lap or means simulating the lap I is then placed on the surface of the lap with its effective abrading surface engaging the effective abrading surface of the lap I and is moved in a sidewise direction over said lap to work the abradant into the surface of the lap I and to cause the excessive abradant to flow into the longitudinal grooves I of said lap. If there is an excessive amount of kerosene or abradant on the lap this may be blotted off through the use of suitable blotting paper or the like.

The crystal 4 is then placed in the opening II and is rested on the relatively fiat end 2| of the portion 20. The said crystal is held in position while the holder 5 is slid onto the surface of the lap in a sidewise direction. After the said crystal and holder have been placed on the surface 2 of the lap I a pressure is exerted on the knob-like member 22 to cause the slide plunger I3 to move downwardly and urge the crystal 4 into engagement with the surface 2 of the lap. The tension resilient means I5 is such that the plate I4, functioning cooperatively with the slide plates I2, will frictionally hold the slide plunger I3 in adjusted position. The pressure is then released on the knob 22 and the holder 5 together with the crystal 4 is moved into a sidewise direction over the surface 2 of the lap I. This causes the abradant on said surface 2 to remove a given amount from the engaging surface of the crystal. Because of the fact that the surface 2| on the end of the plunger I3 and the surface 8 on the base 1 are substantially parallel with each other, substantially equal pressure will be distributed throughout the area of the crystal and will cause the opposed surfaces thereof to be abraded substantially parallel with each other. Periodically during the abrading the crystal is removed and cleansed and is tested in a suitable testing device for determining its oscillating characteristics and frequency. If the crystal is of a slightly lower frequency than desired itis again placed in the holder 5 'on the lap I and an additional amount is removed. By

-iollowing this procedure the crystal may be reduced to the proper thickness to obtain the frequency and oscillating characteristics desired. The crystal, because of the particular arrangement of the holder 5 and lap I, will more positively have its opposed surfaces formed in substantially parallel relation with each other and will therefore be of substantially constant thickness throughout. thereby insuring good working or oscillating characteristics. During the abrading the crystal is first abraded on one side for a given period of time and is then removed from the holder, cleansed, reversed, and again placed in the holder and abraded on the second side for a given period of time. This procedure more positively insures forming parallel surfaces on the crystal. During said periodic removal of the crystal from the holder it is tested to determine its frequency and also to determine its oscillating characteristics. The procedure is somewhat of a cut and try method.

In instances when it is found that a crystal oscillates properly but is of a slightly lower frequency than desired, whereby an additional amount is required to be removed from the crystal in order to raise the frequency of the oscillations, instead of placing the crystal in the holder 5 and abrading the side surfaces of the crystal to remove a very slight amount therefrom, the said crystal as shown in Fig. IV may be grasped at the sides by a suitable holder 23 and may be dipped into a bath 24 of hydrofluroic acid for a given time interval, which experiment will teach is sufficient to remove the proper amount from said crystal to obtain the desired frequency. After each dipping, the crystal is washed in water or other suitable liquid to remove the acid. This avoids the danger of altering the oscillating characteristics of the crystal and provides a modified method of obtaining the desired frequency without further abrading. This latter step is preferably only used when it is found that a crystal has good working or oscillating properties but is of a slightly lower frequency than desired and only a relatively small amount of material is required to be removed from the crystal. This latter dipping of the crystal in an acid bath also thoroughly cleanses the crystal. This is essential to the proper operation thereof. Although hydrofluoric acid has been set forth as the preferable acid for the bath it is to be understood that any other known acid which will have an etching effect on the crystal may be used.

From the foregoing description it will be seen that simple, efficient and economical means have been provided for accomplishing all of the objects and advantages of the invention.

Having described my invention, I claim:

1. Means for abrading a crystal, said means comprising a holder for use with a lap having a relatively flat effective abrading surface thereon, said holder having a relatively flat surface for engaging the surface of the lap and having a recess in said surface for receiving the crystal to be abraded, a plunger slidably supported in said holder having a portion with a relatively flat end communicating with the crystal holding recess, with the said end disposed substantially parallel with the surface of said holder adapted to engage the lap and means for retaining said plunger in adjusted position, the said holder and plunger being adapted to retain the crystal in engagement with the abrading surface of the lap and being adapted to cause the resultant abraded surfaces on said crystal to be in substantially parallel relation with each other.

2. Means for abrading a crystal, said means comprising a holder for use with a lap having a relatively flat effective abrading surface thereon, said holder having a relatively fiat surface for engaging the surface of the lap and having a recess therein for receiving the crystal to be abraded, plunger means slidably supported in the holder and communicating with said recess and having an end surface initially substantially parallel with the flat surface of the holder adapted to engage and retain the crystal in abrading relation with the effective abrading surface of the lap and being adapted to exert a pressure on and cause the resultant abraded surfaces on said a crystal to be in substantially parallel relation with each other and means for supporting said plunger with its end surface substantially parallel with the surface of the lap.

3. Means for abrading a crystal, said means comprising a holder for use with a lap having a relatively flat abrading surface thereon, said holder having a relatively fiat surface for engaging the surface of the lap and having a recess in said surface of a size and shape to receive the crystal to be abraded and being slightly larger than said crystal, a plunger slidably supported in said holder having a portion with a relatively flat end communicating with the crystal holding recess in said holder and resilient means for retaining said plunger in adjusted position with the relatively flat end thereof in desired relation with the recess of said holder, the said plunger and recess being adapted to retain the crystal in desired abrading relation with the lap.

4. In a device of the character described a holder for use with a lap having a relatively fiat abrading surface thereon and a relatively long slideway in substantially, normal relation with said surface, said holder having a base with a relatively flat surface for engaging the surface of the lap and having a recess in said relatively fiat surface of a size and shape to receive work to be abraded, a relatively long plunger slidably supported in said holder having a reduced portion with a relatively flat end communicating with the recess in said holder adapted to engage the work in said recess when said work and holder are in position on the lap, means for supporting said plunger with the surface of its reduced end substantially parallel with the surface of the lap and being adapted to cause the opposed surfaces of the work abraded while held by said holder to be in substantially parallel relation with each other.

5. Means for abrading an article, said means comprising a holder for use with a lap having an effective abrading surface of a given shape thereon, said holder having a surface thereon for engaging the surface of the lap and shaped substantially to the shape of the surface of the lap and having a recess in said surface for receiving the article to be abraded, a plunger slidably supported in said holder having a portion with an end surface communicating with the holding recess, said end surface being shaped to exert a substantially uniform pressure on the article in the recess substantially throughout the area of said article in the direction of the underlying surface of the lap when the holder is in position thereon and means for retaining said plunger in adjusted position, the said holder and plunger being adapted to retain the article in engagement with the abrading surface. of the lap and being adapted to cause the resultant abraded surfaces on said article to be in substantially coaxial relation with each other.

6. Means for abrading crystals, said means comprising a holder for use with a lap having a relatively flat horiz;ntally disposed effective abrading surface, said holder having a recess therein larger in area than the area of a crystal to be positioned in said recess for engagement with the abrading surface, said holder having a relatively flat surface resting on and gravitation ally held in engagement with the fiat surface of the lap and in substantially flush relation with the surface of the crystal when in engagement with the abrading surface of the lap. a member having a relatively flat surface disposed toward the surface of the lap and in substantially parallel relation with the surface of the lap, adapted to engage the crystal under the action of gravity for distributing a substantially uniform pressure on the crystal throughout the area thereof. said holder and engaged relatively fiat surface of the lap being moveable relative to each other with the crystal being free to move laterally in said recess between the substantially parallel surfaces adapted to engage the opposed sides of said crystal whereby the crystal will move in a nonmniform path about the surface of the lap during the movement of said holder and lap relative to each other and will be simultaneously held so that the resultant opposed abraded surfaces Will be in substantially parallel relation with each other.

'7. Means for abrading crystals, said means comprising a holder for use with a lap having a relatively flat horizontally disposed effective abrading surface with a plurality of grooves therein, said holder having a recess therein larger in area than .the area of a crystal to be positioned in said recess for engagement with the abrading surface, said holder having a relatively flat surface resting on and gravitationally held in engagement with the .flat surface of the lap and in substantially flush relation with the surface of the crystal when in engagement with the abrading surface of the lap, a member having a relatively flat surface disposed toward the surface of the lap and in substantially parallel relation with the surface of the lap, adapted to engage the crystal under the action of gravity for distributing a substantially uniform pressure on thecrystal throughout the area thereof, a loose abradant on the relatively flat surface of the lap between said surface and the engaging surfaces of the holder and the crystal, said holder and engaged relatively flat surface of the lap being moveable relative to each other with the crystal being free to move laterally in said recess between the substantially parallel surfaces adapted to engage the opposed sides of said crystal whereby the crystal will move in a non-uniform path about the surface of the lap during the movement of said holder and lap relative to each other and will be simultaneously held so that the resultant opposed abraded surfaces will be in substantially parallel relation with each other.

CHARLES W. MACCONNELL. 

